As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand for batteries has also sharply increased as an energy source for the mobile devices. Also, much research on batteries satisfying various needs has been carried out.
In terms of the shape of batteries, the demand of prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, the demand of lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, having high energy density, high discharge voltage, and high output stability, is very high.
Furthermore, secondary batteries may be classified based on the construction of an electrode assembly having a cathode/separator/anode structure. For example, the electrode assembly may be constructed in a jelly-roll (winding) type structure in which long-sheet type cathodes and anodes are wound while separators are disposed respectively between the cathodes and the anodes, a stacking type structure in which pluralities of cathodes and anodes having a predetermined size are successively stacked one on another while separators are disposed respectively between the cathodes and the anodes, or a stacking/folding type structure in which pluralities of cathodes and anodes having a predetermined size are successively stacked one on another while separators are disposed respective between the cathodes and the anodes to constitute a bi-cell or a full-cell, and then the bi-cell or the full-cell is wound.
Recently, much interest has been taken in a pouch-shaped battery constructed in a structure in which such a stacking or stacking/folding type electrode assembly mounted in a pouch-shaped battery case made of an aluminum laminate sheet because of low manufacturing costs, light weight, and easy modification in shape. As a result, the use of the pouch-shaped battery has gradually increased.
FIG. 1 is an exploded perspective view illustrating the general structure of a conventional pouch-shaped secondary battery 10.
Referring to FIG. 1, the pouch-shaped secondary battery 10 includes an electrode assembly 30, pluralities of electrode taps 40 and 50 extending from the electrode assembly 30, electrode leads 60 and 70 welded to the electrode taps 40 and 50, respectively, and a battery case 20 for receiving the electrode assembly 30.
The electrode assembly 30 is a power generating element comprising cathodes and anodes successively stacked one on another while separators are disposed respectively between the cathodes and the anodes. The electrode assembly 30 is constructed in a stacking structure or a stacking/folding structure. The electrode taps 40 and 50 extend from corresponding electrode plates of the electrode assembly 30. The electrode leads 60 and 70 are electrically connected to the electrode taps 40 and 50 extending from the corresponding electrode plates of the electrode assembly 30, respectively, for example, by welding. The electrode leads 60 and 70 are partially exposed to the outside of the battery case 20. To the upper and lower surfaces of the electrode leads 60 and 70 is partially attached insulative film 80 for improving sealability between the battery case 20 and the electrode leads 60 and 70 and, at the same time, for accomplishing electrical insulation between the battery case 20 and the electrode leads 60 and 70.
The battery case 20 is made of an aluminum laminate sheet. The battery case 20 has a space defined therein for receiving the electrode assembly 30. The battery case 20 is formed generally in the shape of a pouch. In the case that the electrode assembly 30 is a stacking type electrode assembly as shown in FIG. 1, the inner upper end of the battery case 20 is spaced apart from the electrode assembly 30 such that the plurality of cathode taps 40 and the plurality of anode taps 50 can be coupled to the electrode leads 60 and 70, respectively.
FIG. 2 is an enlarged view, in part, illustrating the inner upper end of the battery case of the secondary battery shown in FIG. 1, in which the cathode taps are coupled to each other in a concentrated state and connected to the cathode lead, and FIG. 3 is a front see-through view illustrating the secondary battery of FIG. 1 in an assembled state.
Referring to these drawings, the plurality of cathode taps 40, which extend from cathode collectors 41 of the electrode assembly 30, are connected to one end of the cathode lead 60, for example, in the form of a welded bunch constituted by integrally combining the cathode taps 40 with each other by welding. The cathode lead 60 is sealed by the battery case 20 while the other end 61 of the cathode lead 60 is exposed to the outside of the battery case 20. Since the plurality of cathode taps 40 are integrally combined with each other to constitute the welded bunch, the inner upper end of the battery case 20 is spaced a predetermined distance from the upper end surface of the electrode assembly 30, and the cathode taps 40 combined in the form of the welded bunch are bent approximately in the shape of V.
As applications to which a secondary battery is applied are diversified, there is necessity for a battery cell constructed in a structure in which the positions of the electrode terminals are adjusted depending upon devices to be used. For the conventional secondary battery, however, the positions of the electrode taps extending from the electrode plates constituting the electrode assembly must be changed to change the positions of the electrode terminals, which is restricted depending upon the specifications of the devices to be used.
When a secondary battery is used as a unit cell of a battery module, on the other hand, the safety of the battery module must be more carefully considered. Generally, a lithium secondary battery suffers relatively great volumetric change while lithium ions are absorbed to or discharged from an anode. Specifically, the lithium secondary battery repeatedly expands and contracts during the repetitive charge and discharge of the lithium secondary battery. At this time, the internal resistance of the lithium secondary battery increases. As a result, the efficiency of the lithium secondary battery is greatly reduced. Also, a battery case may be separated due to excessive expansion of the lithium secondary battery. As a result, an electrolyte may leak, and therefore, the lithium secondary battery may catch fire or explode. Furthermore, the fire or explosion of some battery cells results in consecutive fire or explosion of the remaining battery cells, whereby a serious situation may be caused.
Consequently, there is high necessity for a novel secondary battery constructed in a structure in which the positions of the electrode terminals are easily adjusted and having improved safety.